Monday, May 21, 2018

Long March 4C Sends Chang’e 4 Relay Satellite Toward Moon

A Long March 4C rocket launches with the Chang’e 4 communications satellite bound for the Earth-Moon L2. The satellite will act as a communications relay for the yet-to-be-launched Chang’e 4 lunar lander/rover combo. Photo Credit: Cai Yang / Xinhua

Using a Long March 4C rocket, China launched the first spacecraft of its Chang’e 4 lunar mission along with two smaller satellites. The booster lifted off at 5:28 p.m. EDT (21:28 GMT) May 20, 2018, from Launch Complex 3 at the Xichang Satellite Launch Center in the country’s Sichuan Province.

The rocket carried the Queqiao communication relay satellite planned to be delivered to the Earth-Moon L2 Lagrangian Point located some 280,000 miles (450,000 kilometers) directly “behind” Earth as viewed from the Sun, or some 37,000 miles (60,000 kilometers) beyond the far side of the Moon.

The secondary payload for the mission consists of two radio astronomy satellites, known as DSLWP-A1 and A2. they are embarking on a trip to lunar orbit.

The mission was launched earlier than originally planned as it was targeted for June 2018. The cause of the reschedule remains unknown given that Beijing typically keeps the details about pre-launch preparations and launches under tight wraps.

China has not also disclosed any information regarding the timeline of the May 20 flight. However, what is known is that Long March 4C completed a short vertical ascent after which it started heading into southeastern direction toward East China Sea.

The rocket’s ride to space lasted some 15-20 minutes. During this phase of the mission the first stage of the launch vehicle was dropped over the Guizhou Province, while the payload fairing fell somewhere in the coastal Fujian Province. The second stage was detached over the East China Sea.

The remainder of the mission’s timeline is uncertain as Beijing has not informed the public as to exactly when Queqiao and the DSLWP-A duo are slated to reach L2 and lunar orbit respectively.

Designed by the China Academy of Space Technology (CAST), Queqiao is a communications satellite based on the company’s CAST100 satellite platform. The name of the spacecraft, chosen by China National Space Administration (CNSA) in late April 2018, is derived from a Chinese folktale and means “magpie bridge”.

Weighing around 937 pounds (425 kilograms), Queqiao features two deployable solar arrays and a deployable 13.8-feet (4.2-meter) dish antenna for the relay equipment. It is designed to be operational for more than five years.

The relay communication equipment of Queqiao gives the spacecraft four 256-kilobit-per-second links in X-band between itself and Chang’e 4 lander and rover. Moreover it provides one link in S-band at two megabits per second between the satellite and Earth.

In order to establish a communications link with the yet-to-be-launched Chang’e 4 lunar lander and rover, China will need Queqiao. Any spacecraft on the Moon’s far side would require a relay satellite to transmit signals.

Besides establishing a communications link between Chang’e 4 and ground stations on Earth, Queqiao is capable of providing radio-sky images, frequency dependence of radio in the very-low-frequency band and to perform low-frequency radio astronomical observations. As such, the satellite is fitted with a low-frequency radio detector.

The launch of the lander/rover part of the Chang’e 4 mission is currently scheduled for December 2018. That mission is expected to land on the lunar surface in Von Karman crater in the South Pole-Aitken Basin to investigate an unexplored region of the Moon, as well as to develop technologies required for the later stages of China’s lunar exploration program.

China’s first two lunar missions, Chang’e 1 and 2, were lunar orbiters sent in 2007 and 2010 respectively. Chang’e 3 landed on the surface in December 2013 and deployed a rover that ultimately operated for about two and a half years. The most recent mission in the series—Chang’e 5-T1—launched in October 2014. It served as a technology demonstrator for Chang’e 5 lunar sample return mission, slated to launch in 2019.

Piggybacking on the flight were DSLWP-A1 and DSLWP-A2 (Discovering the Sky at Longest Wavelengths Pathfinder)—two identical micro-satellites manufactured by the Harbin Institute of Technology weighing approximately 99 pounds (45 kilograms) each. Nicknamed Longjiang-1 and Longjiang-2 (meaning “dragon river”), the satellites are planned to be inserted into a lunar orbit at an altitude of 124 by 5,592 miles (200 by 9,000 kilometers).

If everything goes as planned, the twin micro-satellites are expected to be able to conduct ultra-long-wave astronomical observations of the sky at frequencies between one megahertz and 30 megahertz. Observations performed by DSLWP-A1 and A2 could provide insight into the nature of energetic phenomena from celestial sources. Additionally, the probes are also designed to be available for amateur radio tests.

The Long March 4C booster employed for the May 20 launch had an estimated liftoff mass of 250 metric tons. It was 150 feet (54.7 meters) tall with a diameter of 11 feet (3.4 meters). The booster design is capable of delivering payloads of up to 4.2 metric tons into a low-Earth orbit, 2.8 metric tons into a Sun-synchronous orbit, and up to 1.5 metric tons into a geostationary transfer orbit.

Sunday’s launch marked the 275th flight in the Long March rocket family overall and the 15th for China in 2018. The country’s next mission is currently scheduled to take place on June 10, 2018, when a Long March 3A booster is expected to lift off from Xichang with the Fengyun 2H meteorology satellite on board.


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